The present invention pertains to the radio communication art and, more particularly, to a squelch circuit adapted for use in a radio transceiver.
Squelch circuits for use in radio receivers are well known in the communication art. Squelch circuit operation includes monitoring the level of the signal received and processed by the receiver and muting the receiver if this signal does not exceed a certain minimum threshold level. As a result of squelch action, the user of the receiver is not subjected to annoying noise signals which occur in the absence of a received information signal. Squelch circuits are commonly found in amplitude modulated type receivers and are especially suited for use in two-way amplitude modulated transceivers.
A substantial problem with squelch circuits used in prior amplitude modulated receivers is that the squelch often operates on signal fading. That is, an otherwise strong received signal might sometimes fade in level due to an interference in the transmitting medium. If the threshold level for squelch action is set at the same level in both the receiver mute and unmute conditions, the receiver is subject to muting during the fade periods whereby communication to the listener is hampered.
In addition, prior art squelch circuits have not adequately provided for switching transients which occur when an amplitude modulated transceiver is switched from the transmit to the receive mode. During, and after, the switching transition, circuitry within the receiver may produce transient signals which, if not muted, result in an annoyance to the listener.